Carburetor



@CL 29, 1963 H. A. CARLSON ETAL 3,109,043'

CARBURETOR Filed May 2, 1960 5 Sheets-Sheet 1 9 47 fal 32 INVENTORSHAROLD A.CAR| SON OLIN J. EICKMANN ROBERT J. SMITH www ATTORNEY Oct. 29,1963 H. A cARLsON :a1-Al.v 3,109,043

cARBUREToR Filed May 2. 1960 5 sheetshsheef s INVENTORS HAROLD A. CARI.SON OLIN J. HORMANN ROBERT SMITH BY 'l MMM- ATTORNEY 5 Sheets-Sheet 4 'FIG. '7.

/06 F' l G. 8

INVENTORS HAROLD A CARLSON OLIN J. EICKMANN ROBERT J. SMITH ATTOBNEYCARBURETOR H A. CARLSON ETAL Oct 29, 1963 Filed May 2. 1960.

n Oct: 29, 19.63 H. A. CARLSON ETAL CARBURETOR 5 Sheets-Sheet 5 FiledMay 2. 1960 F IG.9.

FIG.|O.

INVENTORS HAROLD A.CARLSON OLIN J. EICKMANN ROBERT J. SMITH BY ATTORNEYUnited States Patent O 3,109,043 CARBURETOR Harold A. Carlson,Brentwood, @lin l. Eickmann, Normandy, and Robert Il. Smith, St. Ann,Mo., assignors to ACF Industries, Incorporated, New York, NSY., acorporation of New Jersey Filed May 2, 1950, Ser. No.V 26,152 10 Ciaims.(Cl. 2131-23) This invention relates to carburetors, and has for anobject the provision of a carburetor structure which is relativelyinexpensive to manufacture and more ellcient and reliable in use.

Another object of the invention resides in the provision of a carburetorcomprising a plurality of individual sections secured together bymechanical fasteners, such as bolts or screws, to facilitate manufactureand assembly.

A further object f the invention resides in the provision of acarburetor comprising an air horn section, a main body section, a fuelbowl section, and a throttle section, the several sections being securedtogether in stacked relationship to form a mixture conduit having mainand primary venturis therein.

Another object of the invention resides in the provision of amulti-section carburetor in which a main fuel systern, a step-up device,and an accelerator pump are located in a depending portion of the mainbody section, said depending portion being disposed within the fuel bowland adapted to be immersed within the fuel contained therein.

Another object of the invention, resides in the provision of main andprimary venturis provided on a main body section formed of metal havinga relatively high coeliicient of heat conductivity, whereby therefrigerating effect due to expansion of fuel and air passing throughthe venturis acts to draw heat from the fuel in the fuel bowl and fromthe depending portion of the main body section, to thereby reduce theformation of vapor bubbles in the fuel bowl, accelerating pump,vacuumeter and main fuel passage.

Another object of the invention resides in the provision of amulti-section carburetor structure in which the fuel bowl section isformed of material having a relatively low coefcient of heatconductivity, such as a thermoplastic or thermosetting plastic, toreduce the passage of heat from the engine to the fuel contained withinthe fuel bowl.

Another object of the invention resides in the provision of amulti-section dual (two-barrel) carburetor structure which issymmetrical about a vertical plane extending longitudinally centrally ofthe structure.

Another object of the invention resides in the provision of a dualcarburetor structure comprising two individual main fuel systems tosupply fuel to their respective mixture conduits under control of acommon fuel metering step-up device responsive to manifold vacuum.

Another object of the invention resides in the provision of a dualcarburetor structure embodying an accelerating pump operable responsiveto throttle movement to supply additional fuel to the mixture conduits,the pump having a fuel inlet disposed at the lower end of the de-,pending portion of the main Ibody section adjacent the bottom of thefuel bowl.

Another object of the invention resides in the provision of a dualcarburetor structure provided with an idle air by-pass to supplyadditional air to the mixture conduit posterior to the throttle valveduring idling operation of an engine at high ambient temperatures, theflow of air through said by-pass being controlled by a temperatureresponsive valve.

The invention embodies other novel features, details of construction andarrangement of parts which are here- Frice inafter set forth in thespecification and claims and illustrated in the accompanying drawings,forming part thereof, wherein:

FIG. l is a side elevation showing an internal combustion engineprovided with a carburetor embodying features of the invention.

PIG. 2 is` a top plan view of the carburetor.

FIG. 3 is a top plan View of the carburetor with the air horn sectionremoved.

FIG. 4 is an elevation showing one side of the carburetor.

FIG. 5 is an elevation showing the opposite side of the carburetor,parts being broken away to illustrate the automatic choke mechanism.

FIG. 6 is an end elevation of the carburetor.

FIGS. 7 and 8 are sectional views taken along the lines 7-7 and 8 8,respectively, of FIG. 2.

FIG. 9 is a fragmentary section illustrating one of the idle fuelsystems. n

PIG. 10 is a fragmentary section taken along the line lll-10 of FIG. 9.

FIG. ll is a fragmentary section illustrating the outlet passage fromthe accelerating pump cylinder.

Referring now to the drawings for a better understanding of theinvention, the canburetor C is shown in FIG. l as mounted upon theintake manifold 2 of an internal combustion engine E. During operationof the engine, a conventional fuel pump P acts to move fuel from a fueltank T through a conduit 3 to the carburetor.

The dual carburetor is shown as comprising an air horn section 4, a mainbody section 5, a fuel bowl section 6, and a throttle section 7, theseveral sections being secured together in stacked relationship by meansof screws 8 to form two identical downdraft mixture conduits 9 9' havingidentical primary venturis lll-10 and main venturis 11-11 therein. Themain body section 5 is formed with two identical annular dependingflanges 12--12 telescopical-ly engaged within annular recesses 13-13formed in the fuel bow-l section 6 to define the main venturis 11--11.The primary venturis lll-10 are supported on struts 14-1-4 integral withthe main body section 5.

An unbalanced choke valve 16 is secured to a choke shaft 17 journaled inthe air horn section 4 to control the flow of air through the air inlet1S into the mixture conduits 9-9. A throttle valve 19' is secured to athrottle shaft Z1 journaled in the throttle section '7, the valve beingmanually actuated by means of a suitable mechanical linkmeans of a link33.

A piston 34 -is mounted in a cylinder 36 having a suction passage 37leading therefrom to a mixture conduit 9, the piston being connected tothe lever 31 by a link 38. A spirally wound birnetal thermostat 39 hasits inner end anchored to a stud 41 and its outer end engaging the lever31. The thermostat 39 acts to bias the choke valve toward its closedposition when the engine is cold and to permit gradual opening of thevalve during warm-up of the engine. The piston 34 acts to move the chokevalve 16 toward its open position responsive to intake manifold vacuum.

A lever 42 is `secured to fthe choke shaft 17 and connected by a link 43to a cam actuating member 45 journaled on a stud shaft 44. A :fast idlecam 46 is also journaled on the shaft de Afor engagement by an idleadjustment screw 4'7 mounted on :the throttle lever 22. The cam `46 isunbalanced to move by gravity in a clockwise direction, as viewed inFIG. 4, and is moved in a counterclocliwise direction by a lug dS on themember 45 responsive to closing of the choke valve 16. A screw 49 isprovided on the throttle section 7` for engagement with the throttlelever 22 to limit closing movement of the throttle valve 19.

The fuel bowl section 6 is formed with an elongated fuel bowl 51 havinga sump 52 therein. r[The fuel bowl section, including the bowl 51, isformed with a flat upper surface for engagement by a flat bottom surfaceon the main body section 5. The main body section is formed with a wall53 which overlies and corresponds to the contour of 'the fuel bowl rim,sai-d wall having a threaded aperture to receive a iioat actuated needlevalve 54. The main body section is formed with a flat upper surface forengagement by the air horn section 4 which has a oat bowl cover portion56 engaging the top surface of the Wall 53.

A float structure 57 is shown as comprising two floats 58-53interconnected by a lloat arm 59 mounted for pivotal movement on a pivotpin 61 which is engaged at its ends in recesses formed the wall 53. Thefloat arm 59 is formed with an upwardly ext-ending finger 62 to move aneedle 63 against a valve seat 64 in the valve body 66 to control thefuel level in the bowl.

The main body section 5 is formed with a depending portion 67 whichextends downwardly into the 'fuel howl 51 and sump 52. The dependingportion 67 is provided with :two identical fuel metering orifices 63-68leading into their respective -main fuel passages or fuel wells 69 69,the passages being provided with fuel nozzles 71 71 to discharge fuelinto their respective primary venturis 1li-10. Apertured tubes 72-72 areprovided in their respective main fuel wells 69-69 for the flow of airpassing from the air inlet 18 through vent passages 73-73, the tubesbeing supported on plugs 74 74 presstted into openings in the main bodysection 5. The ow of fuel through the orifices 68-68 into theirrespective main fuel wells 69-69 is controlled by a step-up devicecomprising a piston 76 having ltwo stepped metering rods 77-77 mountedthereon for vertical movement within ltheir respective orifices to varythe fuel flow therethrough. The piston 76 is mounted in a cylinder 7 8formed in the depending portion 67 and is biased upwardly toward the airhorn section 4 by a compression spring 79. A suction passage 81 leadsfrom the lower end of the cylinder 78 to a mixture conduit 9 posteriorof the throttle valve 19 to cause the piston to be drawn downwardly inthe cylinder responsive to a high vacuum condition posterior of thethrottle valve =19 to thereby lower the metering rods 77 77 to decreasethe rate of fuel How through the metering orifices 68-63.

As illustrated in FIGS. 9 and l0, the rmixture conduits 9 9 are providedwith their respective idle fuel systems comprising idle fuel passages-82 S2 extending upwardly from their respective main fuel passages 69-69and merging with their respective cross passages 83-83 which, in turn,merge with downwardly extending pasn sages Sti-84. The fuel passages S282 are provided with fuel metering tubes 86-86 and air bleed vents 87-87leading to the air inlet 118. The cross passages 8?: 83 are providedwith restrictions 8S 8S between the passages 82 S2 and passages 811-84.Air bleeds 89-89 lead lfrom the air inlet 118 to the upper ends of thepassages 811-84. Idle ports 91-91 and 92-92 lead from `the lower ends ofthe passages 84- 84 to their respective mixture conduits 9 9, the ports92 92 being provided with lidle adjustment screws 93-93.

An accelerating pump structure is provided on the depending portion 67between the floats 58 58, and is shown as comprising a cylinder 94having a fuel inlet 96 and a fuel outlet passage -97 provided with inletand :outlet check valves 98 and 99, respectively. The fuel outletpassage 97 leads to two outlet ports 101 101 located to discharge fuelinto their respective mixture conduits 9 9 adjacent the primaryventur-is 1t} 10.

A piston 102 is mounted in the cylinder 94 and provided with a pistonrod 193 whch extends upwardly through an opening in the cover 56. Ahelical compression spring 164 surrounds the rod 103 Iand is engagedbetween the cover 56 and piston 102 to bias the latter downwardly intothe cylinder. A rocker arm 106 is pivotalfly mounted intermediate itsends on a pivot pin 11217 journaled in a boss 133 on the cover S6, oneend of the arm extending through a slot 109 in the piston rod 103. Theother end of the rocker arm 106 is connected to the throttle lever Z2 bya link 1:11. A throttle return tension spring 112 is secured at one endto the throttle section 7, and at its other end to the rocker arm 106 tobias the throttle valves 19 toward their closed position.

The carburetor is also provided with a hot idle compensator system whichis shown as comprising an air hy-pass 113 extending through the severalsections 4, 5, 6 and 7 to deliver clean air from withi-n an air filterto the mixture conduits 9 9 posterior of the throttle valves 19-19. Theow of air through the by-pass `113 is regulated -by a valve 114 mountedon one end of a bimetal thermostat 116 secured at its other end to abase plate 1117. The base plate 117 is secured to the air horn sec-1tion 4 by screws 118, and is formed with a port 119 having a seat forengagement by the valve 114.

During hot weather and high underhood temperatures, some `of the fuelIi-n the fuel bowl vaporizes and passes upwardly through bowl vents 121into the air filter and tends to enrich the fuel mixture supplied to theengine. To lean out the fuel mixture under such conditions, thethermostat 116 opens the valve 1514 to supply additional air through theby-pass 113 to the mixture conduits When the throttle valves are movedtoward their closed position lfor deceleration or idling of the engine,the piston 76 is moved downwardly by the differential in pressurethereon to compress the spring 79 'and to move the metering rods '77-77into their respective metering orifices 6% 68 to decrease the flow offuel from the fuel bowl into the main fuel wells 69-69.

Vihen the throttle valves 19-19 are moved toward their open positionduring acceleration of the engine, the spring 79 moves the step-uppiston 76 upwardly against the air horn section 4 to raise the meteringrods 77-77 and thereby incre-ase the flow area through the meteringorifices 68-68 to increase the amount of fuel supplied to themain fuelwells 69 69. Y

During acceleration of the engine, the throttleY valve lever 22 actuates:the link 111 and rocker arm 106 to release the piston rod 103 andpermit the spring 104 to move the laccelerator piston 102 downwardlyinthe cylinder 94 to discharge fuel therefrom Ainto the outlet passage97 and thence through the accelerator ports 101 101 into theirrespective mixture conduits 9 9 adjacent the primary ven-turis 10 10.The throttle return spring 112 acts through the rocker arm 106 andpiston rod 103` to raise Ithe piston 102 to draw fuel from the fuel bowlsump 52 through the inlet 96 into the cylinder 94 during movement of thethrottle valves toward closed position.

During starting of a cold engine, the thermostat 39 acts through thelever 29, link 33 and lever 32 to bias the choke valve 16 toward itsclosed position to increase the richness of the fuel mixture supplied tothe engine. When the engine starts firing, the piston 34 acts throughthe link 38, levers 31 and 29, link 33 and lever 32 to urge the chokevalve toward its open position against the resistance offered by thethermostat 39. As the engine warms up, warm air is drawn from a suitablesource through the conduit 27 into the choke housing and thence past thepiston 34 and through the passage 37 to the mixture conduits, posteriorof the throttle valves, thereby causing the thermostat 39 to graduallyopen the choke valve.

An important feature of the invention resides in the utilization of thecooling eect, due to the expansion of the fuel mixture as it passesthrough the venturis, to cool the fuel within the fuel bowl and theseveral passages and cylinders to reduce volatiliziation andpercolation. This result is accomplished by forming the fuel bowlsection 6 of a material of low thermal conductivity, such as a plastic,'and by forming the miain body section S of a material of high thermalconductivity, such as aluminum. When heat is extracted from the venturiportion of the main body section, the temperature of the dependingportion 67 is lowered sufficiently to maintain the fuel in the severalpassages and cylinders in a liquid condition substantially free ofvapors or gases. To reduce icing, the throttle section 7 is formed of ametal of relatively high thermal conductivity adapted -to be heated froma suitable source of heat.

By providing the several fuel systems on the main body section 5, it ispossible to effect a material saving in the cost of manufacture andassembly. It will .also be noted that the needle valve 54, step-upcylinder '78, and accelerator pump cylinder 94 are arranged in a commonvertical plane on the longitudinal axis of the carburetor, and that themixture conduits 9-9 and floats 58-58 are equidistantly spaced onopposite sides of said axis.

Certain structures have been described 'herein which will fulfill lallthe objects of the present invent-ion, but it is contemplated -thatother modifications `will be obvious to those skilled in the art whichcome within the scope of the invention as defined by the appendedclaims.

We claim:

1. A carburetor comprising a body structure formed with -a fuel bowlportion and two mixture conduits, an integral metallic structureincluding a fuel feed section for said carburetor and a differentventuri section coextensive with each one of said mixture conduits, heatinsulating means spacing said body structure from said integral metallicstructure, land means extending within said fuel bowl for maintainingfuel therein at a predetermined level, said fuel feed section includinga plurality of parts thereof spaced from and extending into said fuelbowl, each of said extending parts Ahaving a different terminal endportion positioned below said predetermined fuel level and a differentfuel passage extending from said terminm end thereof through saidmetallic structure to each one of said venturi sections.

2. A carburetor for an internal combustion engine and comprising aplurality of individual sections secured together in stackedrelationship and providing two downdraft mixture conduits, a first oneof said sections comprising a fuel bowl, means within said fuel bowl formaintain-ing fuel therein at 'a predetermined level, a second of saidsections comprising an integral structure formed with ardiferent primaryventuri and a different main venturi in each mixture conduit and adepending portion extending downwardly said fuel bowl below saidpredetermined fuel level and spaced from the walls thereof, heatinsulating means spacing said first section from said second section,said second section formed with two main fuel passages extending throughsaid depending portion, each one of said passages having an outlet pontopening into :a different one of said primary venturis 'and an inletport opening through said depending portion into said fuel bowl belowsaid predetermined fuel level.

3. A carburetor for an internal combustion engine and comprising aplurality of individual sections secured together in stackedrelationship and providing two downdraft mixture conduits, a first oneof said sections comprising a fuel bowl, means within said fuel bowl formaintaining fuel therein -at a predetermined level, a second of saidsections comprising an integral structure formed with a differentventuri in each mixture conduit and a depending portion extendingdownwardly within said fuel bowl below said predetermined fuel level`and spaced from the Iwalls thereof, heat insulating means spacing saidfirst section from said second section, said second section formed withtwo nia-in fuel passages extending through said depending portion, eachone of said passages having an outlet port opening into a different oneof said venturis and an inlet port opening through said dependingportion into said fuel bowl below said predetermined fuel level, a thirdof said sections comprising an air horn section, a fuel bowl coverintegral with said air horn section, an air inlet portion projectingupwardly from said air horn section, a fourth of said sectionscomprising a throttle section engaging the lower side of said onesection and including a different throttle valve mounted in each of saidmixture conduits, and two idle fuel systems comprising idle fuelpassages extending from their respective main fuel passages through saiddepending portion and said first section to idle ports adjacent to saidthrottle valves.

4. A carburetor for an internal combustion engine and comprising aplurality of individual sections secured together in stackedrelationship and providing two downdraft mixture conduits, a firstone ofsaid sections comprising a fuel bowl, means within said fuel bowl formaintaining fuel therein ata predetermined level, :a second of saidsections comprising an integral structure formed with a differentventuri in each mixture conduit and -a depending portion extendingdownwardly within said fuel bowl below said predetermined fuel level andspaced from the walls thereof, heat insulating means spacing said firstsection from said second section, said second section formed with twomain fuel passages extending through said depending portion, each one ofsaid passages having an outlet port opening into a different one of saidventuris and an inlet port opening through said depending por-tion intosaid fuel bowl below said predetermined fuel level, and an acceleratingpump structure including a cylinder formed in said depending portion andhaving Van inlet passage below said predetermined fuel level and anoutlet passage extending through said depending portion to one of saidventuris.

5. A carburetor for an internal combustion engine and comprising aplurality of individual sections secured together in stackedrelationship and providing two downdraft mixture conduits, a first oneof said sections comprising a fuel bowl, means Within said fuel bowl formaintaining fuel therein at a predetermined level, a second of saidsections comprising an integral structure formed with a differentprimary venturi and a different main venturi in each mixture conduit anda depending pontion extending downwardly within said fuel bowl belowsaid predeterminedfuel level and spaced from the walls thereof, heatinsulating means spacing said first section from said second section,said second section formed fwith two main fuel passages extendingthrough said depending portion, each one of said passages having anoutlet port opening into a different one of said primary venturis and aninlet port opening through said depending pontion into said fuel bowlbelow said predetermined fuel level, and a pair of metering rods movablymounted on said second section -with each metering rod extending into adifferent one of said fuel passage inlet ports.

6. A carburetor for an internal combustion engine and comprising aplunality of individual sections secured together in stackedrelationship and providing two downaio-aces draft mixture conduits, afirst one of said sections comprising a fuel bowl, means within saidfuel bowl for maintaining fuel therein a-t a predetermined level, asecond of said sections comprising an integral structure formed with adifferent venturi in each mix-ture conduit and a depending portionextending downwardly within said fuel bowl below said predetermined fuellevel and spaced from the walls thereof, heat insulating means spacingsaid rst section from said second section, said second section formedwith two main fuel pass-ages extending through said depending portion,each one of said passages having an outlet port opening into a differentone of said venturis and an inlet port opening through said dependingportion into said fuel bowl below said predetermined fuel level, a pairof metering rods movably mounted on said second section with eachmetering rod extending into a different one of said fuel passage inletports, a vacuum piston slidably mounted within said depending portion,and means operatively connecting said pis-ton to said pair of meteringrods.

7. A carburetor for an internal combustion engine and comprising aplurality of individual sections secured together in stackedrelationship and providing two downdraft mixture conduits, a differentthrottle valve movably mounted in each one of said mixture conduits, afirst one of said sections comprising a fuel bowl, means within saidfuel bowl for maintaining fuel therein at a predetermined level, asecond of said sections comprising an integral structure formed with adifferent venturi in each mixture conduit and a depending portionextending downwardly within said fuel bowl below said predetermined fuellevel and spaced from the walls thereof, heat insulating means spacingsaid first section from said second section, said second section formedwith two main fuel passages extending upfwardly through said dependingportion, each one of said passages having an outlet port opening into adifferent one of said venturis and an inlet port opening into said fuelbelow said predetermined fuel level and a fuel well within saiddepending portion [intermediate said ports, and means forming yadifferent idle fuel passage extending from each one of said fuel Wellsand having an idle port in a different one of said mixture conduitsadjacent to said throttle valve therein.

8. A carburetor for an internal combustion engine and comprising aplurality of individual sections secured together in stackedrelationship and providing two downdraf-t mixture conduits, a differentthrottle valve movably mounted in each one lof said mixture conduits, afirst one of said sections `comprising a fuel bowl, means within saidfuel bowl for maintaining fuel therein at a predetermined level, asecond of said sections Icomprising an integr-al structure :formed witha different venturi in each mixture conduit and 'a depending portionextending downwardly within said fuel bowl below said predetermined fuellevel and spaced from the walls thereof, heat insulating means spacingsaid first section from said second section, said second section formedwith two main fuel passages extending upwardly through said dependingportion, each one of said passages having an outlet port opening into adifferent one of said venturis and an inlet port opening into said fuelbelow said predetermined fuel level and a fuel well Within saiddepending portion intermediate said ports, means forming a differentidle fuel passage extending rfrom each one of said fuel wells and havingan idle port in a different one of said mixture conduits adjacent tosaid throttle valve therein, and an accelerating pump structureincluding a *cylinder formed in said depending portion and ya pistonwithin said cylinder, said `depending portion having `an inlet passageto said cylinder below Isaid predetermined fuel level and van youtletpassage extending from said cylinder through said .depending portion toone of said venturis.

9. A carburetor for an internal combustion engine and comprising aplurality of individual sections secured together in stackedrelationship and providing two downdraft mixture conduits, Ia differentthrottle valve movably mounted in each one of said mixture conduits, afirst one of said sections comprising a fuel bowl, means within saidfuel bowl for maintaining fuel therein at a predetermined level, asecond of said sections comprising an integral structure formed with `adifferent venturi i-n each mixture conduit and a depending portionextending downwardly Within said fuel lbowl below said predeterminedfuel level and spaced from the walls thereof, heat insulating ymeansspacing said rst section from said second section, said seco-nd sectionformed with two `main fuel passages extending upwardly through saiddepending portion,

each one olf said passages having an outlet port opening into ladifferent one of said venturis and `'an inlet port opening into saidfuel below said predetermined fuel level and 4a fuel well within saiddepending portion intermediate said ports, means forming a differentidle fuel passage extending from each one of said fuel wells and havingan idle port in a different one of said mixture conduits adjacent tosaid throttle valve therein, an accelerating pump structure including acylinder formed in said depending portion and a piston within saidcylinder, said depending portion having an inlet passage to saidcylinder below said predetermined fuel level and -an outlet passage fromsaid cylinder extending through said depending portion to one of saidventuris, and a pair of metering rods movably mounted on said secondsection with each metering rod extending into a different one of saidfuel passage inlet ports.

10. A carburetor for Ian internal combustion engine and .comprising aplurality of individual sections secured together in stackedrelationship and providing two down-k draft mixture conduits, adifferent throttle valve movably mounted in each one of said mixtureconduits, a first one of said sections comprising a fuel bowl, meanswithin said fuel bowl lfor maintaining fuel .therein at a predeter-kmined level, a second of said sections comprising an integral structureformed with a venturi in each mixture conduit and a depending portionextending downwardly within said fuel bowl below -said predeterminedfuel level and spaced from 4the walls thereof, heat insulating meansspacing said first section from said second section, said second sectionformed with two main fuel passages extending upwardly through saiddepending portion,'each one of said passages having an outlet portopening into a different one of said venturis and an inlet pont openinginto said fuel below said predetermined fuel level and Va fuel wellwithin said depending portion intermediate said ports, means forming adifferent idle fuel passage extend ing from each one of said fuel well-sand having an idle port in a different one of said mixture conduitsadjacent to said throttle valve therein, an accelerating pump structureincluding a cylinder formed in said depending portion yand a pistonwithin said cylinder, said `depending portion having an inlet passage tosaid cylinder below said predetermined fuel level and an outlet passagefrom said .cylinder extending through said depending portion to one ofsaid venturis, a pair of metering rods movably mounted on said secondsection with each metering rod extending into a `different one of saidfuel passage inlet ports, a vacuum piston slidably mounted within saiddepending portion, 'and means operatively connecting said vacuum pistonto said pair of metering rods.

References Cited in the file of this patent i UNITED STATES PATENTS

1. A CARBURETOR COMPRISING A BODY STRUCTURE FORMED WITH A FUEL BOWL PORTION AND TWO MIXTURE CONDUITS, AN INTEGRAL METALLIC STRUCTURE INCLUDING A FUEL FEED SECTION FOR SAID CARBURETOR AND A DIFFERENT VENTURE SECTION COEXTENSIVE WITH EACH ONE OF SAID MIXTURE CONDUITS, HEAT INSULATING MEANS SPACING SAID BODY STRUCTURE FROM SAID INTEGRAL METALLIC STRUCTURE, AND MEANS EXTENDING WITHIN SAID FUEL BOWL FOR MAINTAINING FUEL THEREIN AT A PREDETERMINED LEVEL, SAID FUEL FEED SECTION INCLUDING A PLURALITY OF PARTS THEREOF SPACED FROM AND EXTENDING INTO SAID FUEL BOWL, EACH OF SAID EXTENDING PARTS HAVING A DIFFERENT TERMINAL. 